Figure 1.

The Bun-Madm growth-regulatory complex. Long isoforms of Bun (such as BunA) promote tissue growth in partnership with Madm.
Short Bun isoforms (BunB-E, collectively denoted BunS) can antagonize BunA, thus inhibiting
its function. The existence of other unknown proteins (question marks), such as a
transmembrane receptor protein, that function either upstream or downstream of the
BunA-Madm complex is currently unclear (dashed lines). The mechanism by which the
BunA-Madm complex is regulated probably involves BunA phosphorylation (P). BunA and
Madm are likely to promote growth by controlling transcription and/or protein secretion.